PPMXL Catalog Column Descriptions

PPMXL Overview

PPMXL is a catalog of positions, proper motions, 2MASS- and optical photometry of 900 million stars and galaxies, aiming to be complete down to about V=20 full-sky. It is the result of a re-reduction of USNO-B1 together with 2MASS to the ICRS as represented by PPMX.

For more details, see Roeser, Demleitner, & Schilbach (2010). Background for the USNO-B catalog is given here, while 2MASS documentation is available here.

PPMXL Catalog Column Descriptions

Gator serves the PPMXL Catalog (25 columns, 910,468,710 data rows). The column descriptions can be found below.

Name

Intype

Units

Description

ipix

int8

Identifier (Q3C ipix of the USNO-B 1.0 object)

double

deg

Right Ascension J2000

dec

double

deg

Declination J2000

e_raepRA

real

deg

Mean error in RA*cos(delta) at mean epoch

e_deepDE

real

deg

Mean error in Dec at mean epoch

pmRA

double

deg/yr

Proper Motion in RA*cos(delta)

pmDE

double

deg/yr

Proper Motion in Dec

e_pmRA

real

deg/yr

Mean error in pmRA*cos(delta)

e_pmDE

real

deg/yr

Mean error in pmRA*cos(delta)

nobs

int

Number of observations used. nobs may be NULL for stars coming from ARIHIP or Tycho-2 via PPMX (i.e. bit 1 is set in flags).

epRA

real

Mean Epoch (RA)

epDE

real

Mean Epoch (Dec)

Jmag

double

mag

J selected default magnitude from 2MASS

e_Jmag

real

mag

J total magnitude uncertainty

Hmag

double

mag

H selected default magnitude from 2MASS

e_Hmag

real

mag

H total magnitude uncertainty

Kmag

double

mag

K_s selected default magnitude from 2MASS

e_Kmag

real

mag

K_s total magnitude uncertainty

b1mag

double

mag

B mag from USNO-B, first epoch (see Note 1)

b2mag

double

mag

B mag from USNO-B, second epoch (see Note 1)

r1mag

double

mag

R mag from USNO-B, first epoch (see Note 1)

r2mag

double

mag

R mag from USNO-B, second epoch (see Note 1)

imag

double

mag

I mag from USNO-B (see Note 1)

magSurveys

int

Surveys the USNO-B magnitudes are taken from. Digits assigned to the surveys for b1mag, b2mag, r1mag, r2mag, and imag are concatenated (in that order). Digits are those given in Note h to Table 3 in USNO-B except both 7 and 9 in Note h are 7 here.

From this field, you can also see which of the surveys contributing to USNO-B had positions for the object.

flags

int

bit	meaning
0	One of the coordinates had excessively large chisquare
1	Row is from PPMX. These objects are mostly Tycho stars that were masked out of USNO-B. For these, the USNO magnitudes (b1mag through imag) have special meanings, see Note 1.
2	Row is from PPMX and replaces a single row from USNO-B. This is done when the astrometry from PPMX was better than the astrometry of the corresponding PPMXL object.
3	Row replaces multiple USNO-B objects. When PPMX contains an object that has more than one counterpart in PPMXL, all such counterparts are discarded on the assumption that they should have been matched in USNO-B or result from erroneous matches. For these rows, bit 1 is always 1.

Note 1

Magnitudes from USNO-B should be used with care. Photometric calibration may be severely off for some plates. For objects from PPMX (bit 1 set in flags), these magnitudes have a special meaning as per the following table:

PPMXL column	PPMX column	PPMX content
b1mag	Cmag	Catalogue magnitude from source
b2mag	Bmag	Johnson B magnitude
r1mag	Rmag	calc. Ru magnitude from source
r2mag	N/A	always None
imag	Vmag	Johnson V magnitude